Construction for sea-shore protection against erosion



A. RIVIERE 2,931,183 SEA-SHORE PROTECTION AGAINST EROSION Apnl 5, '1960CONSTRUCTION FOR Filed July 5, 1955 2 Sheets-Sheet 1 April 1960 A.RIVIERE 2,931,183

CONSTRUCTION FOR SEA-SHORE PROTECTION AGAINST EROSION Filed July 5, 19552 Sheets-Sheet 2 1 5 Iii Fig. 5

United States CONSTRUCTION FGR SEA-SHQRE PROTECTHON AGAENST ERUSIDNAndi- Rivicre, Bourg-la-Reine, France Application Juiy 5, E55, SerialNo. 520304 Claims priority, application France .iuly 6, 1954 13 Qlairns.(Cl. 61-3) This invention relates to jetties and more particularly topermeable jetties.

The customary devices or structures heretofore used for protectingseashores against erosion have, in many cases, proved unsatisfactory. Infact, such devices favor an accumulation of sediment on their leesideand at the same time they reject the littoral current seaward promotingthus a dispersion of the sediment in a way similar to that sort ofdispersion which sometimes occurs through the action of currents whichin oceanography are termed rip-currents.

On the leeside of the known structures it is frequently noticed that aturbulent backwash or whirl current occurs which provokes erosionsometimes down to the lowest point of the protective structure staked onthe coast with the result that the sea may pass around such structure.Even more frequently it is noticed that erosion is greater at such partsof the shore construction or structure where the wind blows leeside.

Such drawbacks are serious enough to justify the conclusion that thecustomary shoreline protective structures are sometimes more harmfulthan useful.

Various improvements have already been made to the establishment ofprotective structures: such are, for instance, constructions of thesurbased typeso-called Dutch type-or constructions or structures of theFaraman type. Such device which have proved in certain cases to giveexcellent results may, however, lead in other cases to drawbacks of theabove-described kind. Moreover,- constructions of the Dutch or Faramantype are always rather expensive.

A principal object of the present invention is a new type of protectivestructure to protect a shore having as its main characteristic the factthat it is built in two portions leaving between them a permeable zonewhich 'is preferably a gap or cut extending over the whole of the heightof the construction or over part of its height, e.g. a so-calledcontinental or landward portion well secured into the shore and aseaward portion.

Other features and advantages of the shore protective structure inaccordance with the present invenion will be better understood asdescribed in the following specification and appended claims, inconjunction with the following drawings in which Fig. l is a plan viewof a known type of shore protective structure, and is illustrative ofthe action of such structures,

Fig. 2 is a diagrammatic plan view of a protective structure accordingto the invention illustrating the manner in which the structurefunctions to cause deposition of sediment on both sides of an innerportion of the structure causing the shoreline or beach to grow ratherthan be eroded,

Fig. 3 is a side elevation view of a protective structure of the typeshown in Fig. 2,

Fig. 4 is a plan view of the protective structure shown in Fig. 3,

Figs. 5 through 12 are plan views of shoreline protec- 2,931,183Patented Apr. 5, 1960 ice tive structures according to the invention,and illustrate various configurations of the spaced portions jointlyforming the structure,

Fig. 13 is a side elevation view of a structure according to theinvention and illustrates that the structure portions may be partiallysubmerged and need not extend above the surface of the water throughtheir respective lengths.

As indicated heretofore, known protective shore structures of the solidkind have a serious deficiency in that the leeside of the structure issubjected to turbulent backwash as a result of which the leewardshoreline adjacent the structure is eroded. The reason for suchdefective operation is illustrated diagrammatically in Fig. 1 in which aprotective structure 1 of the solid kind is disposed for protecting ashore or beach 2.. The prevailing incoming swells arrive from thedirection denoted by the arrow H. The direction of the littoral currentis denoted by C and is dispersed to the open sea as dispersive currentsC The leeside of the structure 1 is subjected to turbulent backwash Ccausing an erosion of the shoreline in a leeside area 4.

According to the drawings a shore protective structure in accordancewith the invention is constructed, Fig. 2, as a single continuous innerportion 5A starting at the shore and extending toward the open sea so asto form an angle with the shoreline. This inner portion is impermeableto sediment and has a substantially greater longitudinal dimension thanits transverse dimension. An outer impermeable portion 513 is disposedspaced seawards from the inner portion forming a zone or gap 6 betweenthe two portions which is permeable to sediment. The outer portionpreferably has a greater longitudinal dimension than its transversedimension.

Here again, the direction from which the sea swell is coming is shown byarrow H. The path taken by the shore-current is shown by arrow C Thedirection shown by arrows C is that taken by the sea swell currentarising from the outer portion 5B of the construction. Arrow C shows thedirection taken by the current formed by the wind due to a combinationbetween currents C and C In the hatched areas 7, 8 a build-up of theshoreline has taken place.

The distance between the two portions of the construction has to bedetermined in accordance with the characteristics of the sea swell andthe grade at which the particles are carried away along the littoral.

Under such conditions, repeated observation has shown that, even in casethe displacement of sediment particles remains low or in case thenatural losses by dispersion are very high, build-up increases on eitherside of the construction. Such sort of increase or deposition on bothsides of the construction results in protection of the coast within theactive area of the construction or structure.

The dynamics according to which the construction is operating may beexplained as follows in accordance with what has been proven from testsmade on miniature models:

The so-called continental portion 5A of the construction acts, withrespect to the sediments carried away by the shore stream, in a waysimilar to that which occurs in a customary construction, the shorereceiving in consequence a feed lee-ward at 7;

The swell current which tends to arrive along the oil"- portion orseaward portion 58 is not nullified-as it is in the case of thecustomary construction-by the shorestream which is swerved seaward, butcan develop freely so as to join the latter at gap 6.

Both currents are carrying sediment which they transfer onto the zonelying see-side of the construction so 'as to secure a build-up at 8.

It should be stated that:

The amount of material required for a structure according to the presentinvention is smaller than in the customary forms of construction;

The construction according to the present invention does not give riseto any dispersion of the sediments in an off-shore direction;

The construction according to the present invention is based on aprinciple which is entirely different from the basic idea underlying anyconstruction of frontal, oval, circular or transversally extending type,such as established namely by Faraman.

Figures 3 and 4 which represent respectively a side elevation view and aplan view section, show diagrammatically, by way of example, aconstruction in accordance witht the present invention, all referencefigures being identical with those of Figure 2.

The construction is made up in two straight-line portions of which 5A isthe inner or continental portion and 5B the outer or seaward portion.

The length of gap 6 is of the order of 25% of the total length of theconstruction.

In the embodiment in Figure 5 the outer portion D of the construction orstructure is oifset with respect to the continental portion C, remainingparallel to the latter, so that the centerline of both portions areparallel but oltset. It being understood that the ofiset can be madeeither on one side depending upon the prevailing sea conditions or onthe opposite side.

In the embodiment in Figure 6, the outer or seaward portion D has beenpositioned in a diiferent way than that of the continental portion andits end nearest to the shore has been ofiset with respect to thecontinental portion, either to the left or to the right, at whateverdesired orientation. The two portions have their centerlines so orientedthat projections thereof would intersect forming a complementary pair ofangles which are an obtuse angle and an acute angle.

-In the embodiment in Figure 7, the seaward portion D is situated atright angles with the continental portion C and may occupy with respectto the latter whatsoever desired position.

In Figure 8 the seaward end of the continental portion C ends with afrontal element or bulbous end F. In a same manner the seaward portionDends at its seaward end with a frontal element or bulbous end F1. Saidfrontal element could, moreover, be located at the other end of theseaward or outer portion or the latter might be provided at both endswith bulbous ends. In any of above described embodiments, a frontalelement of any type whatsoever may be provided so that the end soprovided has a more transverse dimension than the opposite end.

As can be seen in Figures 9 through 12 the plan projection of the axisof the outer portion or of the continental portion, or of both of them,may include one or more curves the shallow part of which can bepositioned in a given direction or in the opposite one, the relativepositioning of the two portions, the outer and the inner or continental,being situated as desired, as in the cases previously contemplated. Theheight may vary from one end to the other end of the construction and insome casese it may be contemplated to build the outer portion as well asthe continental portion, or both of them, in the form of a submergedconstruction, in part or in totality. Moreover, it will be noted that inthe embodiments shown in Figs. 5 through 12 the outer portion isdisposed oifset toward the leeward of the seaward end of the innerportion, that is, oflset to leeward of the longitudinal centerline ofthe inner portion.

As willbe seen in Figure 13 in which the sea-level is seen at N, thecontinental as well as the outer portion are both practically submerged.

In certain cases, it may be advantageous to build the outer portion inconformity with or in diiferent positioning from that used for thecontinental portion or even to give it a curved projection or again todivide it into multiple outer portions, not shown.

The gap separating the two portions of the construction may, in somecases, be replaced by a set of pile work or obstacles, or by a portionof submerged construction, so as to slow down the movement of thesediment without, however, stopping it.

The above devices which have been described or shown apply, of course,whatever may be the number and the spacing of such constructions orstructures and Whatever be the form of the edges of the gap or gaps orpervious areas.

Whatsoever mode of construction may be resorted to according to personalpreference: pile planks, masonry, gabionade, ete., since the profile ofthe construction does not interfere practically with the mechanism ofsediment formation.

Such embodiments which have been described by way of non-limitativeexamples may be made use of either separately or in combination, thoughremaining within the objects of the invention.

Specifically the transverse section of the construction may be of anydesired shape, particularly rectangular, as in the examples representedon the appended drawings or in any manner, according to the localconditions, the profiles of the two parts of the structure beingeventually different from each other.

What I claim is:

1. A structure for protecting seashores comprising, in combination, asingle continuous inner portion starting at the shore and extendingtoward the open sea so as to form an angle with the shoreline, saidinner portion being impermeable to sediment and having a substantiallygreater longitudinal dimension than its transverse dimension anddisposed with its longitudinal dimension substantially transverse to theshoreline, a single continuous outer portion disposed spaced seawardsfrom said inner portion in position to form a predetermined zone betweenthe two portions permeable to sediment and through which current flow isdirected in a predetermined direction -for depositing sediment on theshoreline adjacent opposite sides of said inner portion, and said outerportion being impermeable to sediment and having a substantially greaterlongitudinal dimension than its transverse dimension.

2. A structure for protecting seashores in accordance with claim 1, inwhich said inner and outer portions each have a longitudinal centerline,said portions being positioned so that said centerlines aresubstantially in the same plane.

3. A structure for protecting seashores in accordance with claim 1, inwhich said inner and outer portions each have a longitudinal centerline,said outer portion being positioned so that its centerline is in a planesubstantially parallel to a plane coinciding with the longitudinalcenterline of said inner portion.

4. A structure for protecting seashores in accordance with claim 1, inwhich said inner and outer portions each have a longitudinal centerline,said portions being positioned so that said centerlines coincide withplanes intersecting one with the other, and the outer portion beingdisposed to leeward of a plane coinciding with the centerline of theinner portion.

5. A structure for protecting seashores in accordance -with claim 4, inwhich said intersecting planes form with claim 1, in which each of saidportions has a larger transverse dimension adjacent a seaward endopposite end thereof.

8. A structure for protecting seashores in accordance with claim 1, inwhich said seaward end of each portion is bulb-shaped. t-

9. A structure for protecting seashores in accordance with claim 1, inwhich said inner portion is substantially straight and said outerportion is arcuate, and in which the inner portion has a longitudinalcenterline and the outer portion is disposed to leeward of a planecoinciding with said inner portion centerline.

10. A structure for protecting seashores in accordance with claim 1, inwhich said inner portion has ends offset one with respect to the other,and said outer portion is substantially straight and has a straight parthaving a longitudinal centerline, and in which the outer portion isdisposed to leeward of a plane coinciding with the inner portioncenterline.

11. A structure for protecting seashores in accordance with claim 1, inwhich said inner portion has a part adjacent a seaward end thereofconstructed substantially arcuate, said outer portion being arcuate in areverse than the direction with respect to the arcuate part of saidseaward end of the inner portion said outer portion being dis posed toleeward relative to the seaward end of the inner portion.

12. A structure for protecting seashores in accordance with claim 1, inwhich said inner portion has a part thereof adjacent a seaward endconstructed substantially arcuate, said outer portion being constructedsubstantially straight and disposed leeward relative to the seaward endof the inner portion.

13. A structure for protecting seashores in accordance with claim 1, inwhich said inner and outer portions are partly submerged and partlyabove the level of the water.

References Cited in the fileof this patent FOREIGN PATENTS Italy July17, 1937 France June 1, 1955

